1. Field of the Invention
Liquid storage tanks are widely relied upon to preserve and protect their contents. In particular, fuel storage tanks are an important part of the wider energy distribution system, and are routinely called upon to preserve liquid fuels during periods of storage while maintaining the fitness of the stored fuel for dispensation and use on short notice. Fuel storage tanks are commonly used, for example, to store gasoline at a gasoline filling station for distribution to end users, i.e., vehicle operators. Gasoline storage tanks are exposed to a wide variety of environmental conditions, and are often stored underground. Unintentional ingress of environmental moisture is a condition that can be encountered by these tanks.
Gasoline storage tanks often contain a blend of gasoline and alcohol, with a blend having about 10% ethanol (“E-10”) now commonly available as fuel for cars and trucks in the United States and abroad. Ethanol is a hygroscopic material, in that it attracts water from the air or from the surrounding environment. An excess amount of water in the E-10 gasoline/ethanol fuel blend, such as an amount of more than about 0.5% by volume, will result in a condition known as phase separation. When phase separation occurs, excess alcohol, water and some of the lighter parts of the gasoline form a new mixture that is heavier than the gasoline/ethanol blend but lighter than water. This new mixture separates from the E-10 fuel blend and falls to the bottom of the storage tank to form a bottom layer of fluid comprised of approximately 70% alcohol, 20% water and 10% gasoline. If water infiltrates the storage tank quickly, it may settle at the bottom of the tank, below any phase separated fluid, without combining with the ethanol.
Dispenser pumps in fuel storage tanks are typically located near the bottom of the tank. If the alcohol/water/gasoline mixture resulting from phase separation (“phase separated fluid”) forms a thick enough layer at the bottom of the fuel storage tank, the mixture may be pumped into the tank of an end user, such as into an automobile gas tank. As a result, the automobile's engine may fail to start or may run poorly, and the phase separated fluid may have to be removed from the automobile's fuel system at substantial expense. If a layer of substantially pure water becomes thick enough to flow through the pump and into an automobile gas tank, significant damage to the automobile engine may result.
It would be desirable for a gasoline station operator to know whether phase separation and/or water ingress is occurring in the station's fuel storage tank, and particularly for the operator to know whether an alcohol/water/gasoline mixture resulting from the phase separation is at risk of being pumped to a customer.